Process of making di-ammonium phosphate.



S. PEAOOCK. PROCESS 0F MAKING DI-AMMONIUM PHOSPHA'PE.

APPLICATION FILED SEPT. 2, 1909,

Patented June 20, 1911.

SAMUEL PEACOCK, 0F CHICAGO. ILLINOIS, ASSIGNOR T0 'AMERICAN CYNAMID COMPANY, OF NEW YORK, N. Y., A CORPORATION, OF MAINE.

PROCESS OF MAKING, DIAMMONIUM PHOSPHATE.

Specicationof Letters Patent.

Patented lune 2t), 19H.

Application filed September 2, 1909. Serial No. 515,805.

To all whom it may concern: y

Be it known that-l, SAMUEL Pmooon, a citizen of the United States, residing at Chicago, inthe county of Cook and State of lllinois, have invented certain new and useful Improvements in Processes of Making Di-annnonium -Phosphate from Ammonia and lhosphoric Acid; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to ni'ake and use the same.

This invention relatesto a process `for inaking secondary or diammonium phosphate, (Kll,). ,lllt) from ammonia and pl1os phoric acid; and, has for its object to produce a simple and comparatively chea p process t'or making in a single operation, substantially pure commercial secondary ammonium phosphate,`tl1at is more uniform and constanty in compositiim than the products no'w ordinarily sold.

To this end the invention yconsists inthe novel steps and combinations of steps constituting my process, more fully hereinafter disclosed, and particularly pointed out in the claims.

Referring to the accon'ipanying drawing forming a part of this specificatiomin which the figure is a diagrammatic view of an ap paratus embodying the principles of my invention l represents any suitable cooling means for the ammonia gases which enter the absorption system.

ln order to produce secondary or drammonium phosphate free of the primary or mono-ammonium phosphate, by direct combination of a solution of phosphoric acid and cooled ammonia gas, it is necessary to keep the temperature of the solution lbelow 80 degrees centigrade. This l accomplish by passingthe ammonia gases, previously cooled by means of the coil l through the pipe 3, into the tower 2, provided with any suitable cooling means as the coils'll. The phosphoric acid may be placed initially in l the tanks 18, and after the operation has been started the phos horic acid solution 5 trom the discharge o the absorption tower 2, is forced by means of the pump 6 continuously through any suitablecooling means 7,v and through the valved pipe 8, back to the top ot the tower 2, Where it may be passed over the cooling coils 4, and there absorb the ammonia gases entering through the pipe 3.

the phosphoric acid solution.

The unabsorbed gases may be led out of the top of the tower 2, by means of the pipe 9, through a second cooling means 10, and into a second tower 1l, provided with a circulating pump l2, and cooling means 13 for As many towers, cooling coils and pumps may be employed as desired, and the final unabsorbcd gases may be permitted to escape from the last tower by means of the flue 15. The valved pipe 1G connects all the pump circuits in order that should one tower become unduly heated, a cooler solution may at once be supplied from another tower. The circulation of the phosphoric acid solution is continued until a measured quantity of phosphoric acid has neutralized an equivalent quantity of ammonia, for the formation of secondary ammonium phosphate. The total solution from the absorption system is then drawn from the tank 18, and evaporated at, or a few degrees below, SOO C. to the density of crystallization in a vacuum pan using a vacuum not exceeding 350 millimeters'ot mercury. The specific gravity of the solu` tion and therefore the size ot the crystals to be obtained will be determined by the use to which the salt is to be put. Generally, speaking, for commercial purposes largo crystals are desired and these may be produced by employing relatively weaker solutions, thereby causing a slow formation ot the crystals. llt a higher specitic gravity of the solution is employed, the crystals are precipitated faster but are smaller. rlh'e purpose ot thus concentrating the product to the density of crystallization is therefore to etect a separation of the di-annnonimn phosphate inthat solid form which is most desirable for commerce. Further, it will be observed by' keeping the temperature at or bellow-80 C. that no 1nono-ammonium phosphate or trifammonium phosphate is formed in the liquor, which would not be ,the case l`if the solution was permitted to rise. to say 10o above or. tall to say 200 below 80C.

lt, therefore, follows since no 'mono-am monium phosphate nor tri-ammonium phosphate is present in the liquor, that the crystal produced are entirely free from the sa other salts which would not be Ithecasel i* these said salts were allowed in the tirs place to form in the solution. lin othe words, it is evident that, it would beimpo. sible to precipitate vdi-arnmonium phosphate `mixed with the said di-ammonium phos- .froin the primary salts.

yexcept as may be requiredl by the claims.

' NILHZPOM which consists in passing ama suitable chamber; in causing the same to in the presence of other salts without also carrying down some of said other salts adL phate.

As is Well lrnown7 ammonium salts are sold on a guaranteed percentage of ammonia, and are subject to strict State laws. If the commercial product is not of a uniform chemical composition the appraisement is governed by the ammonia content (NH3) of the lowest grade salt the product contains. Therefore it is of great commercial importance to produce the secondary salts as free as possible Of course it Will be understood that those skilled in the art may vary the details of niy process without departing from the spirit thereof, and therefore I do not wish to be limited to the exact minor features set forth,

That T claim is 1. The process of producing di-ammonium phosphate (NHQZHPO4 substantially free from mono-ammonium phosphate monia and phosphoric acid into a suitable l chamber; and in causing the same to react l in the presence of water at a temperature too Il low to permit the formation of the primary salt and in suitably concentrating the solution thus formed under a pressure below that of the atmosphere, substantially as described.

2. The process of producing di-ammonium phosphate substantially free from monoam'monium phosphate, which consists in passing ammonia and phosphoric acid into react in the presence of Water at a temperature too low to permit the formation of the primary salt; in passing the unabsorbed gases into a second chamber and there causing them to react in the presence of water; and in passing the solution from said second chamber into said irst chamber and in suit-l ably concentrating the solution thus formed under a pressure below that of the atmosphere, substantially as described.

3. The process of )roducing di-ammonium phosphate substantially free from monoammoniumphosphate which consists in passing ammonia and phosphoric acid fumes into a suitable chamber; in causing the same to v react in the presence of water, the temperature of which is maintained at a point too low to permit the formation of the primary salt; in assing the unabsorbed gases into a second c amber and causing them to react in the presence of water;` and in constantly circulating the Water solutions through said chambers and in suitably concentrating the solution thus formed under a pressure below that of the atmosphere, substantially as described.

4. The process of producing di-ammonium phosphate substantially free from monoammoniuni phosphate which consists in passing ammonia and phosphoric acid fumes into a suitable chamber, in causing the same to react in the presence of Water the temperaturc of which is maintained through cooling means at a point too low to permit the formation of the primary salt; in passing the n unabsorbed gases into a second chamber and causing them to react 1n the presence of water;.m passing the solution containing the .secondary salt from the second chamber into the first; and in constantly circulating the water solutions through said chambers and in suitably concentrating the solution vthus formed under a pressure below that of the atmosphere, substantially as described.

5. The process of producing di-ammonium phosphate substantially free from monoammonium phosphate which consists in passing ammonia and hosphoric acid fumes through a series of c ambers; in circulating Water solutions of ammonium phosphate through said chambers; in maintaining the temperature in the first chamber at a point too low to permit the primary salt to form; in passing thesolution from the other chambers into said first mentioned chamber and in suitably concentrating the solution thus formed under a pressure below that of the atmosphere; and in recovering the secondary salt thus produced, substantially as described.

In testimony whereof, I ax my signature, in presence of two witnesses.

SAMUEL PECOCK.

Witnesses:

T. A. llrrHEnsPooN, Grao. B. Pirrs. 

